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#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include "main.h"

/* Find least-squares prediction gain for one signal based on another and quantize it */

opus_int32 silk_stereo_find_predictor( /* O Returns predictor in Q13 */

)

{

opus_int scale, scale1, scale2;

opus_int32 nrgx, nrgy, corr, pred_Q13, pred2_Q10;

/* Find predictor */

silk_sum_sqr_shift( &nrgx, &scale1, x, length );

silk_sum_sqr_shift( &nrgy, &scale2, y, length );

scale = silk_max_int( scale1, scale2 );

scale = scale + ( scale & 1 ); /* make even */

nrgy = silk_RSHIFT32( nrgy, scale - scale2 );

nrgx = silk_RSHIFT32( nrgx, scale - scale1 );

nrgx = silk_max_int( nrgx, 1 );

corr = silk_inner_prod_aligned_scale( x, y, scale, length );

pred_Q13 = silk_DIV32_varQ( corr, nrgx, 13 );

pred_Q13 = silk_LIMIT( pred_Q13, -(1 << 14), 1 << 14 );

pred2_Q10 = silk_SMULWB( pred_Q13, pred_Q13 );

/* Faster update for signals with large prediction parameters */

smooth_coef_Q16 = (opus_int)silk_max_int( smooth_coef_Q16, silk_abs( pred2_Q10 ) );

/* Smoothed mid and residual norms */

silk_assert( smooth_coef_Q16 < 32768 );

scale = silk_RSHIFT( scale, 1 );

mid_res_amp_Q0[ 0 ] = silk_SMLAWB( mid_res_amp_Q0[ 0 ], silk_LSHIFT( silk_SQRT_APPROX( nrgx ), scale ) - mid_res_amp_Q0[ 0 ],

smooth_coef_Q16 );

/* Residual energy = nrgy - 2 * pred * corr + pred^2 * nrgx */

nrgy = silk_SUB_LSHIFT32( nrgy, silk_SMULWB( corr, pred_Q13 ), 3 + 1 );

nrgy = silk_ADD_LSHIFT32( nrgy, silk_SMULWB( nrgx, pred2_Q10 ), 6 );

mid_res_amp_Q0[ 1 ] = silk_SMLAWB( mid_res_amp_Q0[ 1 ], silk_LSHIFT( silk_SQRT_APPROX( nrgy ), scale ) - mid_res_amp_Q0[ 1 ],

smooth_coef_Q16 );

/* Ratio of smoothed residual and mid norms */

*ratio_Q14 = silk_DIV32_varQ( mid_res_amp_Q0[ 1 ], silk_max( mid_res_amp_Q0[ 0 ], 1 ), 14 );

*ratio_Q14 = silk_LIMIT( *ratio_Q14, 0, 32767 );

return pred_Q13;

}